Abstract Background: Artificial Reproductive Technologies (ART) and conception following a period of untreated infertility (> one year) are independently associated with increased pregnancy complications in both singleton and multiple pregnancies. It is unknown if placental dysfunction associated with macroscopic and/or microscopic histological discrepancies might explain some of these variances. Aim: To compare the histopathology of placentae from singleton pregnancies belonging to three groups: conception as a result of ART; spontaneous conception (< one year of trying); conception following untreated infertility (> one year). Methods: Pathological examination of placentae from singleton pregnancies of non smoking, age-matched primiparous women with no significant medical history and no known uterine congenital anomalies was performed by a single pathologist blind to the groups. Features were compared using ANOVA and Chi-Square tests. Results: A total of 89 placental pathology reports were available (Control=39, Infertility=17, ART=33). The mean placental thickness was significantly higher in the ART group when compared to the spontaneous conception group (p=0.02). There were significantly more placental haematomas in the ART group (p=0.04) compared to the other groups. There were no significant differences in rates of abnormal placental shapes or abnormal cord insertions. There were no statistically significant differences in the incidence of microscopic placental lesions. There were no statistically significant differences in the incidence of macroscopic and microscopic placental lesions between the infertility group and the other groups Conclusion: Placentae of ART pregnancies show significantly increased thickness and a higher incidence of haematomas. Increased placental thickness has previously been linked to increased perinatal risk.